Transmission system



2 Sheets-Sheet l INVENTOR ATTORNEY MN MN. v J @EN MSN @BWM NNN C. C.TAYLOR TRANSMISSION SYSTEM Filed Jan. l0, 1935 C. 22g/Zw# mi; A/ Ih.ll...- IMW Y (PQPP Sept. 1l, 1934.

2 Sheets-Sheet 2 Sept. 11, 1934. c. c. TAYLOR TRANSMISSION SYSTEM FiledJan. 1o'. v1932 Gai/:Decrease Operator Patented Sept. 11, 1934 Price?1,973,027 y TRANSMISSION SYSTEM Charles Chance Taylor, Flushing, N. Y.,lassignor to American Telephone and Telegraph Company, a corporation ofNew 4York Application January 10, 1933, Serial No. 651,024` n 'zclaime(Cine-44.)

This invention relates to voice-operated devices used with radiotelephone systems or other channels for the transmission of intelligenceand more particularly to arrangements for intercon- 5 necting two ofthese devices in one terminal thereby securing improved operation. Thisis obtained by novel circuit arrangements whereby the action of onevoice-operated device is changed by the faulty action of a second devicein such manner as to eliminate the said faulty action thus making theoperation more nearly automatic and reducing the cost of operating thesystem.

As is well known, a radio vtransmitter and- 'radio receiver may beconnected by means of a combination of four-Wire and two-wire circuitsto a two-wire terminal at a switching point where connections may beestablished by a switching operator between the radio channel andvarious telephone circuits. It is also Well known that terminalamplifiers, voice-operated devices and other apparatus under the controlof the technical operator may be associated with the four-Wire circuitin such a manner that 'echoes and singing, which might be caused byradio or wire line unbalances, are effectively eliminated, and radiationby the radio transmitter of signals received by the radio receiver isprevented. This will be spoken of as the antisinging device hereafter.It is also well known that one of the chief functions of the technicaloperator is to constantly regulate the transmitted speech volume therebymaintaining uniform percentage modulation of the radio transmitter. Avoice-operated gain-adjusting device has been developed to automaticallyregulate this transmitted speech volume thereby relieving the technicaloperator of this duty. This will be spoken of as the gain-adjustingdevice hereafter. In accordance'vvith this invention circuitarrangements' are provided whereby the gainadjusting device and theanti-singing device are so interconnected that improved operation of theanti-singing device is obtained and an objectionable feature of theoperation of the gain-adjusting device is-eliminated.

In more detail, the operation of the gainadjusting device was such thatwhen the switchboard operator had been talking at high volume preparinga call and then told the subscriber to go ahead difficulty wasexperienced if this subscriber cameV in at low volume. The gain ofgain-adjusting device would have been adjusted to a lowlvalue bytheoperator and the o action ofthe device would Vnot permit this gain to beincreased until the end of a two-second period. The subscriber duringthis :period might not b'e able to operate the anti-singingf device andconversation could .not getstarted. This period of tie-up might beconsiderably eX-' 604 tended by either the operator speaking again or bythe receiving side of the anti-singing device operating under control ofthe subscriber at the distant end of the circuit who was also at-.tempting to begin the conversation. Itis well known that faultyoperation of the transmitting side of the anti-Singing device may occurif. it does not secure suiicient speech volume; 'When this faultyoperation occurs this invention causes the gain of the gain-adjustingdevice to increase y very rapidly until suicient speech volume reachesthe anti-singing device to assure its operating satisfactorily. Then theoperation of the gain-adjusting device again becomes normal. This actionremoves theV difficulty rexperienced in Starting va conversation .andalso tends to correct faulty operation: of the. anti-singing device fromother causes. The action is limited to. the lower half of the gain rangeof the gainadjusting device thereby avoiding difiiculties which linenoise operation might produce. The invention may noWbe more fully underfstood from the following description together with theaccompanying-drawings in the Figures 1 and 2 of which the invention isillustrated.` 85 Fig. 1 constitutes a circuit diagram of'one terminal ofa radio telephone system such as might be used in transatlantic'systems'. jFig. 2 is a circuit diagram illustrating in greater detailthe voice-operated gain adjusting device shown schematically in Fig. 1.Similar reference characters have been used to denote like parts in-allof the figures. It is expected that the other terminal will have similararrangements. These terminals might likewise be used on submarine cablesor other communication channelsand it is understood'that the inventionis not to be n limited to radio telephone systems." Referring `to Fig.1, nSL designatesfthe two- Wire line connecting the control' terminal to.the 100 switchboard. The two-wire line, SL,'is connected through ahybrid coil HB1 `to a transmitting path, TL1, and ar'eceivingV path RL1,being-bal.-

anced by a Suitablenetwork N1: IvThefpz/Lth TL1l and the following parts`ofithe transmitting cirv cuit include the line amplifier :TA1 which,ispart of the gainfadjusting device, hybridcoil HB2; transmitting pathTLz, transmitting, path TL3, transformer T1 and radio transmitter RT:The receiving pathincludes radio receiver BR,

vice comprises the variable-gain line amplifier VTA1 and its associatedregulating devices, filter'.

F1, gainv increase operator amplifier detector, gain increase reduceramplifier detector, gain increase disabler, gain decreaserand relaysGIR,

GID, MGR, GRR, and RV. These devices will be described in more detailhereinafter.v

In order that when transmission is taking place over either thetransmitting or receiving path the other path will be disabled, .echo orsinging suppressor devices are associated with each. path. We havecalled'these arrangements the anti-singing device. l'Iheecho suppressorassociated with thel transmitting path TL1 comprises anamplifier-detector unit TAD of well known type with its input connectedthrough band pass filter F2 and variable attenuator TSC to hybrid coilHB2 in conjugate relationship with transmitting Vpath TL2, the output ofamplifier TA1 being balanced by a suitable network N2. The output 'ofthe amplifier-detector unit controls through master relay TMA the relaysTSS and TEI-IO for performing operations incident to the blocking ofdisabling operations whereby transmission is permitted in only one ofthe paths '-IL2 and RL1 at a time. Normally transmission path TL2 isdisabled by the back contacts of relay TSS which short-circuit theconductors, and transmission from transmission path TL1 to the radiotransmitter cannot take place. Blocking means comprising transformerarrangements T2 and T3 are associated between receiving lines RL1 andRL2. These disabling means comprise transformer arrangements which areso connected as to bel balanced when the contacts of relay TEHOare'opened, there-l by preventing transmission through thetransformerarrangements. When the contacts of relay .TEHO are closed, however, thetrans-- former circuits instead of being balanced are in effectconnected so as to be parallel-aiding, thereby permitting transmissionto take place readily. Normally, relay TEHO, which is controlled by theamplifier-detector TAD, is deenergized so that the receiving path isunblocked to permit transmission to take place from receiving path RL2to the two-wire line SL. The input of an amplifier-detector arrangementRAD is connected through band-passlter F4 and receiving sensitivityYcontrol RSC to hybrid coil HB3 inconjugate relationship with receivingpath RL1, and has in its output a relay RM which when operated opens thecontrolcircuit from the amplier-detector TAD to switching relays TSS andTEHO, thereby maintaining the transmitting path TL2 blocked, andreceiving path RL1 unblocked when signal currents are being receivedfrom the radio' receiver.

The operation' of the apparatus so `far described v'for.signaltransmission is as follows: Signal-currents incoming over thetwo-Wire circuit SL passthrough the hybrid coil. HB1 and through thevvariable-gain amplifier TA1. of the energy enters theamplifier-detector unit TAD and causes relays TM, TSS and TEHOto beenergized. Relay TSS removes the short cir- Some cuit from transmittingline TL2, while relay TEHO by opening its contact causes the transformerarrangements T2 and T2 to block the receiving path. In the meantime apart of the energy passes from hybrid coil HB2 through transmittingpaths TL2 and TLS to radio transmitter RT and is transmitted to thedistant terminal. The receiving amplifier detector RAD associated withthe receiving paths cannot now be actuated to disturb the circuitcondition now existing because the receiving path is disabled in themanner already described.

` If in the normal condition of the circuit a signal is received byradio receiver RR, the resulting signalsl pass through receiving pathRL2 and transformer arrangements T2 and T3. The energy divides in hybridcoil HB2, part of the energy passing through receiving amplifier RA1 andhybrid coil HB1 to the two-Wire line SL. Ihe remaining received energypasses through receiving sensitivity control RSC to theamplifier-detector RAD, to cause the operation of relay RM which opensthe circuit controlled by the amplifier-detector unit TAD, therebypreventing energization of relays TSS and TEHO, so that the transmittingpath is disabledand the receiving path remains unblocked so long as thesignal currents are being received.

Referring to Fig. l, the operation of the voiceoperated gain-adjustingdevice is as follows: Signal currents incoming over the two-wire circuitSL pass through the hybrid coil HB1 and are impressed on the input ofthe variable-gain amplifier TA1.` The gain of the amplifier TA1 is socontrolled that regardless of the speech volume at. its input, withinlimits, the speech volume at its output is maintained constant at acertain definite volume which We Will call reference volume. The gainadjustment necessary to secure the reference volume output occurs asfollows: The gain of the line amplifier varies with the .C bias placedon the first two vacuum tube stages. When the grid voltage is low thegain is high. The grid voltage is under the control of the other partsof the circuit, namely, the gain increase operator, gain increasereducer, gain increase disabler and gain decreaser devices. Thesedevices are well known inthe art and are shown in more detail in Fig.2.V

Part of the Vvoice currents at theinput pass throughra Vband pass filterF1 into the gain increase operator, operating the gain increaser relayGIR. These same currents act on the gain increase reducer but have onlya slight effect thereon because ofv their intermittent nature. However,on steady tones or noise the gain increase reducer Will bias the gainincreaser relay GIR in the direction to prevent operation on small noisecurrents. The gain increase operator may comprise a combination ofpotentiometers, amplifiers, and a detector. A low pass lter (not shown)may be provided inthe detector output for the purpose of cutting` offpeaks of noise. The gain increase reducer'may comprise a combination ofpotentiometers, amplifiers and detectors. The detector apparatus may beso biased thatvit Will effect the relayfGIR only on steady tones, suchas noise, but not on speech currents which are intermittent in nature.The gain increaser relay GIR operates the master gain relay MGR providedthe gain increase disablerrelay GID is not operated. The master gainrelay charges the gain regulatingl condenser GRC from battery throughresistances RRi and RR2, the charge GCI being in the direction toproduce a voltage which opposes the :fixed grid battery voltage frombattery FGB. This effectively reduces the grid bias on thel lineamplifier and increases the gain. The voltage on the gain regulatingcondenser GRC also acts as a plate potential for the last tube of thegain decreaser.

The output of the line amplifier divides, part of it .entering the gaindecreaser and gain increase disabler circuits. The gain decreaser mightvinclude a potentiometer and a detector tube so adjusted as to operateon a volume from TA1 above reference volume, but not below. The gaindecreaser draws plate current from the gain regulating condenser GRCwhenever the output of the line ampliiier TA1 goes above referencevolume and thereby discharges this condenser through its plate-filamentcircuit, increasing the negative grid bias on the line ampliiier anddecreasing the gain. The gain increase disabler will include a dischargetube nlled with a gas such as neon. This tube will have its constants soadjusted that it will break down when the output from TA1 is atreference volume. When thegas iilled tube of the gain increase disablercircuit breaks down the GID relay will operate. This will open thecircuit for MGR relay and release it, thus serving to prevent any gainincrease of TA1. The operation of GID will connect a ground to thecondenser 1i) connected tothe grid circuit of the gas iilled tube in thegain increase disabler device. This will increase the sensitivity of thegain increase disabler by 11/2 db. When the gas filled tube ceases todischarge, the condenser 11 in the plate circuit thereof will be chargedthrough the winding of relay GID. This will prevent the relay GID fromreleasing for a period of two seconds after the discharge ceases in thegas lled tube. In this manner once the output reaches reference volumethe gain of the line amplifier remains constant provided the volume doesnot go above reference volume or drop more than 11/2 db. below referencevolume for a period greater than two seconds. If the low volumecondition occurs the GID relay releases permitting the master gain relayto operate, thereby increasing the gain until the output again reachesreference volume.

A relay RV operated by relay RM of the antisinging device disables thegain decreaser and causes the operation of the gain increase disablerrelay GID during the time received speech is operating the anti-singingdevice relay RM, thereby preventing gain adjustment by the echoes oi thereceived speech. The operation of relay GID in this instance is causedby the removal of the grid bias by the opening of left hand contact ofrelay RV. After each operation of the RV relay the GID relay remainsoperated for the two-second period. The fact that the GID relay does notrelease until after a period oi' two seconds following a drop in outputvolume or an operation of the anti-singing device'relay RM has causeddifficulty in getting conversation started. This action is necessary toprohibit the line amplifier TA1 gain from following too rapidly thevariations in speech level, thereby removing some individuality from thevoice and to assist in preventing echoes of received speech fromadjusting the gain of the line amplifier TA1. v

The gain rate relay GRR operates from the plate current of the iirststage of the line amplifier when the gainisabout half `of its maximumand with the .gain regulating condenser, therefore, partially charged.The operation ofv this relay speeds up the condenser charge by reducingresistance in'series with the plate battery through short circuitingresistance RRg, thereby providing a more nearly constant rate of gainchange over, the entire'rangep-Thefoperation of` relay GRR will openthecircuit for relays A, B and Cwhen the-gain of TA1 is onehalf` of itsmaximum. This will prevent the auxiliary` charging circuit forcondenserGRC from being completed-under conditions pointed out hereinafter. Y ilThe invention may new be more fully understood by considering theaction of relays A, B and C oi Fig. 1 as .they interconnect theantisinging device with the gain-adjusting device. They form the subjectof this invention and may be called the quick gain-increaser circuit.This circuit increases the gain oi the gain-adjusting device veryquickly if that gain is in the lower half of its range. conditions withrelay RM non-operated, the gain increase relay GIR operates but thetransmitting anti-singing device relay TM dees not operate. Theoperation When relay GIR is not operated batteries 12 and 13 will havelike poles connected to the circuit including the winding of relay Cv.and relay C will remain inoperated. When the relay GIR operatesbattery 13 is removed from Ythis circuit and relay C will be operated bybattery 12, over contact of relay GRR,. and contacts oi" relay A and B.Relay C when operated will rapidly increase. the gain of the lineamplifier TA1 by charging the gain regulating condenser .GRC throughresistance RRs. Relay C operates from battery through the left-handcontacts of relays` GER, A and B to groundv through resistanccs R1, whenthe left-hand contacts of relay GIR are open. Closing the left-handcontacts of relay GIR again short circuits relay C and it cannotoperate. Relay A operates in series with relays TEI-IO and TSS whenrelay 'I'M operates. Relay B operates in series with relay RV both beingenergized when relay RM operates. Relay GRR operates for the upper halfof the gain range of line amplifier TA1 and is non-operated for thelower half of the gain range. Relay C then operates when relay GIRoperates but relays A, B and GRR are non-operated. This means that relayC will not operate when relay A operates simultaneously with relay GIRor as long as `the transmitting anti-singing relay TM is operatingnormally. Relay B prevents operation of relay C when relay GIR isoperated by echoes of the received voice currents which have operatedrelay RM thereby disabling relays TEHO, TSS, and A to prevent theiroperation by such echoes. This prevents quick gain adjustment by echoesof received speech. Relay GRR limits the quick-gain increase to Vthelower half of the gain range of line amplier TA1. This is very necessaryin limiting any undesirable results of the rapid increase in gain causedby this circuit if false Yoperation of the gain increase relay GIRshould occur from noise currents.

Under suchis then as follows;V

This circuit tends to prevent initial ellenicak toa low value bythe:switchboard operator talking at a high volume and a subscriberimmediatel-y tries to talk at .a .low volume. Without the quick gainincreaser circuit the'gain of the gain-adjusting :device cannot beincreased for two seconds afterspeech ceases or falls below a certain.output volume-because of the hangovero the gain'increase disablerrelay. This same hangover is involved after each operationr of thereceiving anti-singing relay 'RM. The quick gain increaser circuiteliminates this hangover and increases .the gainv of the gain-adjustingdevice very rapidly if signals are operating the GR Vrelay but faulty ornonoperation of the transmitting anti-'singing relay TM is occurring.When normal operation of relay'. TM is secured the quick gain increasercircuit no longer unctions and the operation of the gain-increasercircuit is normal.

While the invention has lbeen disclosed as embodied in certain specicarrangements which are deemed desirable, it is' understood that it iscapable of embodiment in many and other widely varied forms withoutdeparting `from the VTVil spirit of the invention as defined by theappended claims.

` What is claimed is: v f

1. In a transmission system,Y a transmitting channel and a receivingchannel, a voice operated anti-singing device connected' to saidchannels designed so that energy transmitted to or over one of saidchannels will cause the device to disablethe' other of said channels, avoice operated gain adjusting device associated with said transmittingchannel and designed to'adjust the gain a predetermined normal rate, andauxiliary means operated independently of the output volume of saidvoice operated 'gain adjusting device for causing said voice operatedgain adjusting device to vary the gain at a rate faster 'than saidpredetermined normal rate, said auxiliary means being operative when theenergy coming into said gain adjusting device falls suddenly to a levelinsuicient to operate said anti-singing -l device.

ln a tra emission system, atra-nsmitting channel and a receivingchannel, a voice operated antinsingi-ng device connected'. to saidchannels designed so that energy transmitted to or over one ci saidchannels will cause the device to disable the other of said channels, avoice fuera-ted gain adjusting device associated with id transmittingchannel, said voice operated gain adjusting device including a vacuumtube loss device having its cathodefanode circuit in clude-dv in saidtransmitting channel and slow releasing means operated by the energyvolume on the transmitting channel beyond said lvacuumpredeterminedperiod caused bythe slow releaseV of slow releasing meansy after saidenergy volume on the transmitting channel falls below said predeterminedlimits and when said energy volume is insuiicient to operate saidanti-singdevice.l

3. In a transmitting system, a transmitting channel and a receivingchannel, a voice op# erated anti-singing devicevr connected to saidchannels, said device including a relay associated with .saidtransmittingchannel and re' sponsi've to energy volume transmittedthereover, a normally closed short vcircuit across said transmittingchannel, and a control circuit completed by said l.relay `for openingsaid `short circuit, a voice operated .gain adjusting device associatedwith said transmitting. channel, auxiliary means forV rapidlyincr-.easing the gain oi said .voice operated gain adjusting device, andmeans controlled bythe completion of .said con-V trolcircuit insaidantisingingdevice orxpreventing the functioning .oi ysaid auxiliarymeans.

i. In a .transmission'system, a transmitting channel anda receivingchannel, a voice op erated anti-singing device connected to channels,said device including a relayassociated with said transmitting channeland responsive to .energy volume transmitted thercover and acontrolcircuit completed Iby said relay for rendering said .transmittingchannel operative, a voice operated gain adjusting device associatedwith said transmittingY channel, said gain. ad-V justing deviceincluding a :vacuum tube loss ldevice having its cathode-.anode circuitincluded in'said transmitting channel, a condenser for varying .thepotential on the grid .of .said tube device to .control the loss causedby said device, a gain increase rela-y '.operated .by energy 'cominginover said ltransmitting channel to said Vtube device, a lchangingcircuit closed .by said relay for increasing the potentialon saidcondenser to decrease the loss .or .said tube device, a gain increasedisabler` relay operated by the energy volume on said transmitting.channel beyond said vacuum tube 4device when said energy volume iswithin certain limits, means controlled by said gain increase disablerrelay when operated for holding lopen said charging vcircuit for saidcondenser, an lauxiliary :charging `circuit for lincreasing thepotential on said condenser to reduce the loss of said tube device, said.auxiliary charging circuit being completed vby the operation oi saidgain increase relay, and means controlled by the completion of saidcontrol circuit in said anti-singing Idevice vfor holdingr open saidauxiliary charging circuit.

5. In a transmission system, a `transmitting channel and a receivingchannel, a voice voperated anti-singing device connected to -saidchannels, said device including a relay associated with said receivingchannel and responsive to energy volume transmitted thereover and acontrol circuit completed by the operation of said relay, a voiceoperated gain adjusting device associated with said transmittingchannel, said l gain adjusting device including a vacuum tube lossdevice having its cathode-anode circuit included in Asaid transmittingchannel, a -condenm ser for varying the potential on the grid or saidtube device to control the loss caused by said device, a gain increaserelay operated by energy coming'in Vover said transmitting channel tosaid tube device, a charging circuit closed by said relay,` forincreasing the potential on said condenser to decrease the loss of saidtube device, a gain increase disabler relay adapted to be operated bythe energy volume on ysaid transmitting channel beyond said vacuum tube,de` vice when said energy volume is within certain limits, meanscontrolled by said gain increase disabler relay when operated forholding open said charging circuit for said condenser, an auxiliaryYcharging circuit for increasing the potential onsaid condenser toreduce the loss of said tube device, said auxiliary charging circuitbeing completed by the operation of said gain increase relay, and meanscontrolled by the completion of said control circuit in saidanti-singing device for holding open said auxiliary charging circuit andfor operating said gain increase disabler relay.

6. In a transmission system, a transmitting channel and a receivingchannel, a voice operated anti-singing device connected to saidchannels, said device including a relay associated with saidtransmitting channel and responsive to energy volume transmittedthereover and a control circuit completed by said relay for renderingsaid transmitting channel operative, a voice operated gain adjustingdevice associated with said transmitting channel, said gain adjustingdevice including a vacuum tube loss device having its cathode-anodecircuit included in said transmitting channel, a condenser for varyingthe potential on the grid of said tube device to control the loss causedby said device, a gain increase relay operated by energy coming in oversaid transmitting channel to said tube device, a charging circuit closedby said relay for increasing the potential on said condenser to decreasethe loss of said tube device, a gain increase disabler relay operated bythe energy volume on said transmitting channel beyond said vacuum tubedevice When said energy volume is Within certain limits, meanscontrolled by said gain increase disabler relay when operated forholding open said charging circuit for said condenser, an auxiliarycharging circuit for increasing the potential on said condenser toreduce the loss of said tube device, said auxiliary charging circuitbeing completed by the operation of said gain increase relay, meanscontrolled by the completion of said control circuit in saidanti-singing device for holding open said auxiliary charging circuit, again rate relay included in the plate circuit of said vacuum tube lossdevice, said gain rate relay being adjusted to operate when the loss ofsaid tube device is approximately one-half of its maximum, and meanscontrolled by the operation of said gain rate relay for preventing thecompletion of said auxiliary charging circuit for said condenser.

7. In a transmission system, a transmitting channel and a receivingchannel, a voice operated anti-singing device connected to said channelsdesigned so that energy transmitted to or over one of said channels willcause the device to disable the other of said channels, a voice operatedgain adjusting device associated with said transmitting channel anddesigned to adjust the gain at a predetermined normal rate, andauxiliary means operated independently of the output volume of saidvoice operated gain adjusting device for causing said voice operatedgain adjusting device to vary the gain at a rate faster than saidpredetermined normal rate, said auxiliary means being operative onlywhen said voice operated anti-singing device and said voice operatedgain adjusting device are not operated substantially at the same time.

CHARLES C. TAYLOR.

